Area Forecast Discussion
Issued by NWS Paducah, KY

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000
FXUS63 KPAH 201112
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
612 AM CDT Sun May 20 2018

.UPDATE...
Updated aviation section for 12z taf issuance

&&

.SHORT TERM...(Today through Tuesday night)
Issued at 322 AM CDT Sun May 20 2018

The main forecast concern is the strength and timing of convection
over the next few days. Overall model performance is likely to be
poor given the small-scale convective features that have already
muddled up the synoptic pattern.

Over the past 12 hours, widespread convection has altered the
temperature and moisture profiles over the mid-section of the
nation. As mentioned in the 06z SPC day 1 outlook, the 00z model
initializations were poor at several raob sites. In addition, a
surface meso-high over the lower Ohio Valley was not initialized
by the guidance. This all reduces confidence in the 00z model
suite. This includes the hi-res cam models, which did not
accurately depict the convection near the Kansas/Missouri border
at 06z.

Today and tonight, a series of 500 mb shortwaves will track
northeast from the southern Plains into the Missouri Valley.
Virtually all model guidance generates convection over our region,
but the timing and intensity varies. Given the lack of confidence
in any one model solution, the forecast will contain broad-brush
chance pops through tonight. The highest hourly pops will be
shaded toward the late afternoon and early evening hours, when the
peak contribution from diurnal heating occurs. For what its worth,
the high-res cam models target western Kentucky for the greatest
convective potential later this afternoon and early this evening.

Despite the recent convective overturning, it appears ample
sunshine and soupy dew points near 70 will allow the atmosphere to
become quite unstable again this afternoon. This should again
facilitate a few strong convective cores, with isolated hail and
gusty winds.

As for the Monday and Monday night forecast, the synoptic pattern
favors a continuation of thunderstorms chances. A 500 mb shortwave
will track eastward from the upper Mississippi Valley. A surface
boundary is forecast to approach from the north. Once again,
mesoscale convective features will likely play havoc with the
timing of precip. The forecast will maintain the highest pops
Monday afternoon, but only around 50 percent due to the potential
for residual clouds or cooling from overnight or early morning
convection.

On Tuesday, weak upper-level height rises are forecast in the wake
of the Great Lakes shortwave. However, a residual surface cold
front or outflow boundary could stall near the lower Ohio Valley.
Weakening flow fields suggest that any convection Tuesday will be
less organized than previous days. A small chance pop will
continue in the forecast Tuesday. Dry conditions are finally
forecast Tuesday night as 500 mb heights rise and the low levels
stabilize.

.LONG TERM...(Wednesday through Saturday)
Issued at 322 AM CDT Sun May 20 2018

Models continue to show a frontal boundary lingering across the
middle Mississippi/lower Ohio valleys Wednesday through Friday. This
will result in mainly daytime convection each day.  ECMWF and GFS
show the front just south of or in southern portions of the PAH
forecast area Wednesday and Thursday, which will keep any convection
mainly focused in southern and western portions of our region.  By
Friday, the front lifts northward and convection chances will be
area wide Friday afternoon.

After a lull Friday evening, models show low pressure over the Great
Lakes dragging a cold front toward the middle Mississippi valley on
Saturday.  Scattered showers and thunderstorms will spread from west
to east across the PAH forecast area late Friday night into
Saturday.

Unseasonably warm and humid conditions will persist through the
extended.  Dew points will remain in the middle to upper 60s through
the period.  Highs will be in the middle top upper 80s with lows in
the middle to upper 60s.

&&

.AVIATION...
Issued at 612 AM CDT Sun May 20 2018

Main aviation concern is timing of thunderstorms today and tonight.
There is little in the way of concrete guidance to assist with this
concern. Instability will increase during the day today, which will
gradually increase thunder chances. The best odds appear to be in
the 18z to 03z time frame, but thunder cannot be ruled out anytime
in the warm and humid air mass. Gusty winds and heavy rain are
possible in stronger storms, but it is premature to specify when
these will occur in the tafs. Outside of storms, vfr conditions and
light south winds will continue through tonight.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$

SHORT TERM...MY
LONG TERM...RST
AVIATION...MY



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